ci: Add trigger rule for `scarthgap` release

Automatically trigger pipeline for the target branch on meta-cassini.

Signed-off-by: Ali Can Ozaslan <ali.oezaslan@arm.com>

.gitlab-ci.yml

@@ -13,7 +13,8 @@ variables:
   META_CASSINI_TARGET_BRANCH:
     value: none
     description: Comma separated list of meta-cassini branch to trigger
-                 (none, main, nanbield-dev, mickledore-dev, kirkstone-dev)
+                 (none, main, scarthgap-dev, nanbield-dev,
+                 mickledore-dev, kirkstone-dev)
   META_CASSINI_BUILD_IMAGE:
     value: all-images
     description: Comma separated list of images to build

.gitlab/ci/rules.yml

@@ -73,6 +73,9 @@
     - if: '$CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "main"'
       variables:
         META_CASSINI_TARGET_BRANCH: 'main'
+    - if: '$CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "scarthgap"'
+      variables:
+        META_CASSINI_TARGET_BRANCH: 'scarthgap-dev'
     - if: '$CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "nanbield"'
       variables:
         META_CASSINI_TARGET_BRANCH: 'nanbield-dev'